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The larval morphology of the marine bryozoan Bowerbankia gracilis (Ctenostomata: Vesicularioidea)

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Summary

The larval morphology of the marine bryozoan Bowerbankia gracilis has been investigated by light and electron microscopy. The barrel-shaped larva (200 μm long and 150 μm in diameter) is light yellow without any apparent eyespots, although it is positively phototactic during its brief free-swimming existence. The primary morphological characteristics of the larva are: (1) a large corona that forms most of the larval surface, (2) a small apical disc without blastemas, (3) a deep pallial sinus lined by an extensive pallial epithelium, (4) an internal sac without regional specializations, and (5) a polypide rudiment in the oral hemisphere. This organization is characteristic of larvae of the ctenostome superfamily Vesicularioidea, and differs radically from the organization of all other bryozoan larvae examined. The major morphological differences occur in the size and organization of the apical disc, the pallial epithelium, and the internal sac. In most bryozoans, these regions of the larval epithelium represent rudiments of the polypide and the body wall epidermis of the ancestrula. The oral polypide rudiment, the extensive pallial epithelium, and the reduced internal sac in vesicularioid larvae indicate that their pattern of metamorphosis also differs radically from the metamorphoses of other bryozoans.

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Abbreviations

AB:

aboral

acr:

axial ciliary rootlet

ad:

apical disc

anc:

aboral nerve cord

ANT:

anterior

arm:

apical retractor muscle

b:

basal body

bf:

basal foot process

c:

corona

cc:

ciliated cleft

ce:

centriole

ci:

cilium

cl:

cupiform layer of the polypide rudiment

cp:

ciliary pit

cr:

ciliary rootlet

enr:

equatorial neural ring

g:

glandular cells of the pyriform organ

gl:

glycocalyx

go:

Golgi complex

gr:

granule

hcr:

horizontal ciliary rootlet

ic:

intercoronal cell

igf:

inferior glandular field

ip:

infrapallial cells

is:

internal sac

jp:

juxtapapillary cells

l:

lipid droplets

L:

lateral

m:

mesenchyme

m′:

Type I mesenchyme cell

m″:

Type II mesenchyme cell

m‴:

Type III mesenchyme cell

mb:

median band of the polypide rudiment

mc:

marginal cells of the apical disc

mi:

mitochondria

mr:

microridge

mv:

microvilli

nn:

nerve nodule

np:

neural plate

nu:

nucleus

O:

oral

oce:

oral ciliated epithelium

op:

opening to the internal sac

ovc:

oral vesicular collarette

p:

papilla of the pyriform organ

pa:

pallial cell

pe:

pallial epithelium

po:

pyriform organ

POS:

posterior

pp:

parasagittal patches of undifferentiated cells

pr:

polypide rudiment

rer:

rough endoplasmic reticulum

sc:

supracoronal cells

sg:

secretory granules

sgf:

superior glandular field

sp:

suprapallial cells

tc:

terminal cone

tf:

transitional filaments

u:

undifferentiated cells

va:

vacuole

vc:

vesicular cell

wc:

wedge-shaped cells of the apical disc

y:

yolk granule

za:

zonula adhaerens

Gp:

Glutaraldehyde-phosphate

Os:

Osmium

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Author notes

  1. Christopher G. Reed

    Present address: Museum of Comparative Zoology, Harvard University, 02138, Cambridge, MA, USA

Authors and Affiliations

  1. Department of Zoology, University of Washington, 98195, Seattle, WA, USA

    Christopher G. Reed & Richard A. Cloney

  2. Friday Harbor Laboratories, 98250, Friday Harbor, WA, USA

    Christopher G. Reed & Richard A. Cloney

Authors
  1. Christopher G. Reed
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  2. Richard A. Cloney
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Reed, C.G., Cloney, R.A. The larval morphology of the marine bryozoan Bowerbankia gracilis (Ctenostomata: Vesicularioidea). Zoomorphology 100, 23–54 (1982). https://doi.org/10.1007/BF00312198

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  • DOI: https://doi.org/10.1007/BF00312198

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